Question: Right versus left The design of controls and instruments affects how easily people can use them. A student project investigated this effect by asking 25 right-handed students to turn a knob (with their right hands) that moved an indicator. There were two identical instruments, one with a right-hand thread (the knob turns clockwise) and the other with a left-hand thread (the knob must be turned counterclockwise). Each of the 25 students used both instruments in a random order. The following table gives the times in seconds each subject took to move the indicator a fixed distance. Note that smaller times are better.
(a) Explain why it was important to randomly assign the order in which each subject used the two knobs.
(b) The project designers hoped to show that righthanded people find right-hand threads easier to use, on average. Carry out a test at the 5% significance level to investigate this claim.